There are proposed several methods of producing birefringence patterns. JP-A-3-141320 (“JP-A” means unexamined published Japanese patent application) discloses use of a patterned birefringent product possibly visualized as it is held between two polarization plates in a method of recording an image. In JP-A-3-141320, use is made of a technique using a heat mode laser or thermal head to apply heat to the image-forming portion of an anisotropic film, thereby completely or partially reducing the anisotropy.
However, patterns produced by techniques in which birefringence is reduced with heat, as set forth above, all have the drawback of poor heat resistance. That is, there is a risk that when heat is applied to a portion in which birefringence remains, the birefringence of that portion will end up decreasing. Further, in techniques employing thermal heads or the like, since it is difficult to impart difference between the thermal conductivity in the direction of thickness and the thermal conductivity in the in-surface direction, it is extremely difficult to create a pattern at a resolution lower than the thickness of the film. Heating with a laser permits the creation of high-resolution patterns, but there is a problem in that the drawing of fine patterns by scanning with a laser is time-consuming.
JP-A-3-141320 also proposes the technique of lowering the birefringence by using a photodecomposing photopolymer or a photoisomerizing polymer with light. However, the resistance to light of the pattern that is produced by this technique is low, rendering the pattern unsuitable as a birefringence pattern for use in optical elements in particular.
Another technique for producing birefringence patterns has been proposed in the form of the method of applying a coating liquid comprising polymerizable liquid crystals and a polymerization initiator on a support having an alignment film, conducting patterned exposure through a photomask to the coating liquid wherein the liquid crystals are in an aligned state, fixing the alignment of exposed regions by polymerization, applying heat to create an isotropic phase in unexposed regions, and conducting exposure a second time to cause only those regions exposed the first time around to exhibit optical anisotropy (see British Patent No. 2,394,718A, and “Advanced Function Materials”, pp. 791-798, 16, 2006). However, in this method, controlling the state of alignment of the liquid crystals prior to fixation requires conducting multiple exposures while carefully controlling the temperature of the overall system, presenting a problem in the form of a demanding manufacturing process.